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所属分类：.NET技术
C#中提供了IObservable<T>接口和IObserver<T>接口来实现观察者模式，IObservable<T>相当于Subject（主题）接口，下面我们就以代吗来说明下如何利用.net框架提供的观察者模式接口。
WeatherData类包含气温，湿度，气压等属性。
class WeatherData { /// <summary> /// 气温 /// </summary> public string temperature { get; set; } /// <summary> /// 湿度 /// </summary> public string humility { get; set; } /// <summary> /// 气压 /// </summary> public string pressure { get; set; } }
WeatherDataPublisher类实现了IObservable接口，实现了Subscribe订阅方法。
class WeatherDataPublisher : IObservable<WeatherData> { List<IObserver<WeatherData>> observers = new List<IObserver<WeatherData>>(); /// <summary> /// 订阅主题，将观察者添加到列表中 /// </summary> /// <param name="observer"></param> /// <returns></returns> public IDisposable Subscribe(IObserver<WeatherData> observer) { observers.Add(observer); return new Unsubscribe(this.observers, observer); } /// <summary> /// 取消订阅类 /// </summary> private class Unsubscribe : IDisposable { List<IObserver<WeatherData>> observers; IObserver<WeatherData> observer; public Unsubscribe(List<IObserver<WeatherData>> observers , IObserver<WeatherData> observer) { this.observer = observer; this.observers = observers; } public void Dispose() { if (this.observers != null) { this.observers.Remove(observer); } } } /// <summary> /// 通知已订阅的观察者 /// </summary> /// <param name="weatherData"></param> private void Notify(WeatherData weatherData) { foreach (var observer in observers) { observer.OnNext(weatherData); } } /// <summary> /// 接收最新的天气数据 /// </summary> /// <param name="weatherData"></param> public void ReciveNewData(WeatherData weatherData) { Notify(weatherData); } }
下面我们建立一个抽象类WeatherDisplayBase实现了IObserver接口，所有的天气展示板（观察者）继承这个抽象类，需实现OnNext方法，即接收到新数据推送后要进行的数据处理展示工作，并且可重写OnCompleted，OnError方法。
abstract class WeatherDisplayBase : IObserver<WeatherData> { public virtual void OnCompleted() { } public virtual void OnError(Exception error) { } public abstract void OnNext(WeatherData value); }
CurrentConditionDisplay类为当前天气状况展示板，继承WeatherDisplayBase抽象类，展示最新的天气数据。
class CurrentConditionDisplay : WeatherDisplayBase { public override void OnNext(WeatherData value) { Console.WriteLine("------------------"); Console.WriteLine("当前天气状况板"); Console.WriteLine(string.Format("温度：{0}n湿度：{1}n气压：{2}", value.temperature, value.humility, value.pressure)); } }
StatisticsConditionDisplay类为气温统计展示板，继承WeatherDisplayBase抽象类，展示历史最高温度，最低温度，平均温度。
class StatisticsConditionDisplay : WeatherDisplayBase { List<float> temperatures = new List<float>(); public override void OnNext(WeatherData value) { float temperature; if (float.TryParse(value.temperature, out temperature)) { temperatures.Add(temperature); } Console.WriteLine("------------------"); Console.WriteLine("温度统计板"); Console.WriteLine(string.Format("平均温度：{0}n最高温度：{1}n最低温度：{2}", temperatures.Average(), temperatures.Max(), temperatures.Min())); } }
使用方法
class Program { static void Main(string[] args) { WeatherDataPublisher publisher = new WeatherDataPublisher(); CurrentConditionDisplay currentDisplay=new CurrentConditionDisplay(); StatisticsConditionDisplay statisticsDisplay = new StatisticsConditionDisplay(); //订阅当前天气展示板 IDisposable currentDisplayUnsubscriber= publisher.Subscribe(currentDisplay); //订阅气温统计展示板 IDisposable statisticsDisplayUnsubscriber = publisher.Subscribe(statisticsDisplay); for (int i = 0; ; i++) { WeatherData weatherData = new WeatherData(); Console.WriteLine("请输入温度,湿度,压力"); string input = Console.ReadLine(); var array= input.Split(','); weatherData.temperature = array[0]; weatherData.humility = array[1]; weatherData.pressure = array[2]; Console.WriteLine(""); //将输入的新的天气数据传给天气数据发布器 publisher.ReciveNewData(weatherData); Console.WriteLine("============================="); } } }
